Examination of the molecular basis for the action of parathyroid hormone (PTH) is being conducted. The projects proposed are the following: (1) automated synthesis of several new fragments of PTH which contain amino acids beyond residue 34, culminating in the total automated synthesis of the native hormone (84 amino acids); (2) biological characterization of the new fragments including receptor binding properties, agonist and antagonist actions in the renal membrane adenylyl cyclase bioassay, and the in vivo actions in the kidney, including the anticalciuric and phosphaturic actions of PTH; (3) a complete 2D NMR study first of the 1-34 amino terminal fragment of PTH and, subsequently, additional studies of the native hormone, to examine a proposed model for the folding of these peptides in solution, to determine the secondary structure of the peptides, and ultimately to lead to significant new information about the tertiary structure of these peptides; (4) purification of three kidney membrane proteins which have been shown to bind PTH specifically and are thus candidates for receptors; (5) microsequencing the purified receptor candidates and synthesizing peptides which reflect these sequences for use in raising monoclonal antibodies against the receptors; and (6) finally, purification of large amounts of the receptors using immunoaffinity chromatography methods, so that functional reconstitution studies can be conducted to directly examine the biological function of the isolated proteins. These studies will provide new information about the structural features required for the interaction of PTH with its biologically important receptors, and will ultimately lead to the production of agonists and antagonists of the hormones which can be used to treat abnormalities of calcium and phosphate metabolism.